LiPos › LiPo ratings explained: S, mAh and C
LiPo ratings explained: S, mAh and C
The label on a LiPo has three numbers that matter: cell count (S), capacity (mAh) and discharge rate (C). Here is what each means and how to use them.
S: the number of cells
The S number is how many cells are connected in series. Each LiPo cell is nominally 3.7 V, rises to 4.2 V when fully charged and should not be drained below about 3.3 V in normal use (BYU's combat robotics guide gives these figures; never let a cell fall under 3.0 V). So:
| Pack | Nominal voltage | Fully charged |
|---|---|---|
| 1S | 3.7 V | 4.2 V |
| 2S | 7.4 V | 8.4 V |
| 3S | 11.1 V | 12.6 V |
| 4S | 14.8 V | 16.8 V |
| 6S | 22.2 V | 25.2 V |
Your model's speed controller, motor and flight controller are built for a voltage range. Use the cell count your model specifies. Too many cells can destroy electronics; too few leaves it underpowered.
mAh: capacity
mAh (milliamp hours) is how much charge the pack stores. A 2200 mAh battery can in theory supply 2.2 A for an hour. Higher capacity means longer run time but also more weight and size. Capacity also tells you the charge rate. BYU's guide sets charge current from capacity: 1 A is 1000 mA, so a 500 mAh battery charges at 0.5 A (a 1C rate). Do not charge faster than the maker recommends.
C: discharge rate
The C rating describes how quickly the pack can safely supply current, as a multiple of its capacity. As a rough guide, maximum continuous current is capacity in amp hours multiplied by the C rating. For a 2200 mAh (2.2 Ah) pack rated 30C, that is about 66 A. Makers' C ratings are sometimes optimistic, so treat them as a headline number and leave plenty of margin. Choose a pack that supplies more current than your model draws, and use a pack that doesn't get hot in use.
Watt-hours
Watt-hours (Wh) measure total energy. This matters for travel. The CAA says if the Wh rating is not printed on the battery you can work it out: volts × amp-hours = Wh, or for mAh, (volts × mAh) ÷ 1000 = Wh. A 3S 2200 mAh pack: 11.1 × 2200 ÷ 1000 ≈ 24.4 Wh. See flying with lithium batteries for the limits.
Other numbers you may see
- P (parallel): a 3S2P pack has two sets of cells in parallel for more capacity.
- Connector type: XT60, XT30, JST and others. Always use the right plug, not a makeshift adapter.
- Balance lead: the small multi-pin connector used for balance charging.
- Weight: matters in planes and drones.
How to pick a pack
- Check your model's manual for the cell count and capacity range.
- Pick capacity for the run time and weight you can accept.
- Choose a C rating that comfortably covers peak current.
- Make sure it physically fits and balances correctly.
- Buy from a reputable seller and check the charger supports the pack.
Then see charging, storage and the main LiPo guide.
This is general information, not a substitute for the instructions that came with your battery and charger. If your manufacturer's advice differs, follow the manufacturer.
Frequently asked questions
What does 3S mean?
Three cells in series, giving a nominal 11.1 V and 12.6 V when full.
Is a higher C rating always better?
Not necessarily. You need enough for your model's current draw. Ratings are often optimistic, so leave margin.
How do I work out watt-hours?
Multiply volts by amp-hours, or volts times mAh divided by 1000, as the CAA explains.
Can I use a different cell count to my model's spec?
No. Use the cell count the electronics are designed for.